Surface treated vacuum material and a vacuum chamber having an interior surface comprising same

ABSTRACT

A method for the surface treatment of vacuum materials reduces the H 2 O sticking probability on the surface of the vacuum material. The H 2 O sticking probability is reduced by selectively depositing silicon oxide, for example, and covering the regions which are in an active state on the surface of the vacuum material, and by setting the coverage to less than 100% of the state where film formation is achieved. If the abovementioned coverage is within the range from 40 to 80%, then it is possible to reduce the H 2 O sticking probability to a minimum.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application corresponds to Japanese Patent Application Nos.10-249219 and 11-226934, filed in Japan on Aug. 19, 1998 and Aug. 10,1999, respectively, the entire contents of which hereby incorporatedherein by reference. This application is a divisional of U.S. Ser. No.09/460,725, Filed on Dec. 14, 1999, now U.S. Pat. No. 6,316,052, andwhich is a continuation-in-part of U.S. Ser. No. 09/322,162, filed onMay 28, 1999, now abandoned, the entire contents of which are herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention, relates to a method for the surface treatment ofvacuum materials, and more particularly, it relates to a method for thesurface treatment of vacuum materials which are used, for example, invacuum apparatus for thin film deposition purposes in whichsemiconductors and electronic parts are produced.

2. Description of Related Art

In the past, it has been necessary with vacuum materials such asstainless steel which are used in vacuum apparatuses for thin filmprocessing purposes, for example, to reduce the amount of gas which isreleased from the surface of the materials and to reduce the gassticking probability of the surface. Water (H₂O) which is always presentand which has a strong oxidizing action is especially important as sucha gas. A surface treatment which can reduce the “amount of H₂O released”and reduce the “H₂O sticking probability” is very desirable. The “amountof H₂O released” signifies the amount of water which is released fromthe surface into the space when a vacuum material which has been presentin an environment at atmospheric pressure is pumped out to a vacuumenvironment. On the other hand, the “H₂O sticking probability” signifiesthe proportion of the H₂O which does not rebound, but rather sticks tothe surface of the vacuum material when H₂O is colliding with thesurface of the vacuum material in the vacuum environment.

The units of the “H₂O sticking probability” reflect the number of H₂Omolecules that will stick. For example, an “H₂O sticking probability” of2×10⁻³ means that two H₂O molecules out of each one thousand moleculeswill stick.

Much research has been carried out into methods of surface treatment forreducing the “amount of H₂O released”, and some of these methods havebeen put into practical use. These are generally methods in which thesurface of the vacuum material is polished wherein an undesirablemodified surface layer is removed either mechanically or chemically.Conversely, coating methods in which a film which has desirableproperties is formed over the whole surface of the vacuum material arealso in general use. Examples of such films include Cr₂O₃ films(chromium oxide films) obtained by oxidizing the surface of the materialitself, Si films (silicon films and silicon oxide films), and TiN films(titanium nitride films) which are obtained by deposition from theoutside, and BN films (boron nitride films) which are obtained bydiffusion from within the material. Cr₂O₃ films have been disclosed inJapanese Unexamined Patent Applications (Kokai) H6-41629 and H6-116632,silicon oxide films have been disclosed in Japanese Unexamined PatentApplication (Kokai) H4-337074 and BN films have been disclosed inJapanese Unexamined Patent Applications (Kokai) H7-62431 and H4-263011.

Conventional surface treatments, as described above, are all carried outto reduce the “amount of H₂O released”, and their effect has beenevaluated just on the basis of the extent of the “amount of H₂Oreleased”. The other factor, namely the “H₂O sticking probability”, hasnot been evaluated at all. This is mainly because it is very difficultto measure precisely the “H₂O sticking probability”, but it is alsobecause it was thought generally that the two values were proportional,which is to say that the “H₂O sticking probability” should also fall asa result of a surface treatment which reduces the “amount of H₂Oreleased”.

An example of an investigation of surface treatment methods whichmeasure the value of the “H₂O sticking probability” precisely is foundin Japanese Unexamined Patent Application (Kokai) H9-91606. According tothat application, the “H₂O sticking probability” is reduced by heatingstainless steel in a specified atmosphere. However, care must be takenwith handling the material after the treatment and, moreover, the valuesachieved are not satisfactory.

OBJECTS AND SUMMARY

An object of the present invention is to provide a practical method forthe surface treatment of vacuum materials with which the “H₂O stickingprobability” is reduced satisfactorily.

The importance of the “H₂O sticking probability” on the vacuum materialsused in vacuum apparatus for thin film processing, for example, will bedescribed first of all.

The main component of the residual gas in a vacuum apparatus beforebaking (heating while pumping out and de-gassing) is H₂O, and thepressure in the vacuum apparatus before baking is determined principallyby the “amount of H₂O released”. However, when baking the vacuumapparatus, the H₂O pressure falls by a few orders of magnitude. Hence,for a vacuum apparatus which has once been subjected to baking, the“amount of H₂O released” becomes virtually insignificant. The latestvacuum apparatus for thin film processing purposes for the production ofsemiconductors and electronic parts is usually provided with a load-lockmechanism, and once baking has been carried out and the pressure hasbeen reduced, the apparatus is operated continuously for a few weeks oreven a few months while being maintained in a vacuum state. Thus, theeffect of the “amount of H₂O released” is only seen when the vacuumstate has been broken for maintenance purposes and the system is putback into service after it has been exposed to atmospheric pressure.

On the other hand, even when baking has been carried out and the H₂Opressure has been reduced, a large amount of H₂O is released from thesurface as a result of irradiation with energy beams or plasma, forexample, and if the H₂O pressure increases at such a time, then it isknown that a very long period of time is required to return to theoriginal pressure. The amount of H₂O which is released at this time andthe time taken to recover are determined mainly by the magnitude of the“H₂O sticking probability”. Thus, if the “H₂O sticking probability” ishigh, then a large amount of H₂O sticks to the wall, and the time takenfor the H₂O which has been released into the space to reach the exhaustport is also considerable. In such a case, the pumping efficiency isalso poor. Now, energy beams and plasma are certainly generated in thefilm deposition operating state when cleanliness is essential in thinfilm processing. Hence, it is not the “amount of H₂O released” but the“H₂O sticking probability” which is the greatest problem in the thinfilm processing of semiconductor and electronic part production.

Accordingly, the method for the surface treatment of vacuum materials ofthis invention is intended to lower the H₂O sticking probability on thesurface of the vacuum material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a chart which shows the relationship between the “amount ofH₂O released” and the “H₂O sticking probability”.

FIG. 2 is a chart which explains the silicon oxide coverage dependenceof the “H₂O sticking probability” obtained with the method of surfacetreatment of the invention.

FIG. 3 is a drawing which shows, in essential outline, a model of amaterial surface on which silicon oxide has been deposited.

FIG. 4 is a drawing which shows a first embodiment of a processingapparatus for executing the method for the surface treatment of a vacuummaterial of the present invention.

FIG. 5 is a drawing which shows the chemical formula of thetetra-ethoxysilane, which is the source material used in the firstembodiment of the present invention.

FIG. 6 is a drawing which shows a second embodiment of a processingapparatus for executing the method for the surface treatment of a vacuummaterial of the present invention.

FIG. 7 is a drawing which shows the chemical formula of thehexamethyldisiloxane, which is the source material used in the firstembodiment.

DETAILED DESCRIPTION OP THE PREFERRED EMBODIMENTS

1. The Mechanism Behind the “H₂O Sticking Probability”

As mentioned earlier, the importance of the “H₂O sticking probability”has been investigated and the inventors have already disclosed a novelmethod for the precise measurement of the “H₂O sticking probability”(Journal of Vacuum Science & Technology A, Vol. 16, No. 3, p. 1131(1998)). The mechanism behind the “H₂O sticking probability” on thesurface of stainless steel, which is the most usual vacuum material, andmethods of reducing the “H₂O sticking probability” were bothinvestigated using this disclosed method for measuring the “H₂O stickingprobability”.

The mechanism behind the “H₂O sticking probability” is thought to be asindicated below on the basis of the current state of research. The siteswhere gas sticks to (is adsorbed on) a solid surface are calledadsorption sites, and in the simplest model these adsorption sites aredirectly above each of the atoms from which the surface is constructed.The density of these sites is around 10¹⁵ per cm². According to pastresearch it has been confirmed that when a large amount of H₂O isadsorbed, the number of H₂O adsorption sites is also about 10¹⁵ is percm². The state where a large amount of H₂O has been adsorbed correspondsto a surface under atmospheric conditions and so this is the value forthe adsorption sites which contribute to the “amount of H₂O released”.However, ultimately the “amount of H₂O released” is related not to justthe amount of water sticking to the outermost surface (the surface indirect contact with the space on the outside), but also to the strengthof adsorption, the absorption and diffusion of water in the surfacelayer of the micron order (the region extending from the surface down toa certain depth), and the microform of the surface, for example. On thisbasis, the density of the adsorption sites is also the same when theamount adsorbed, corresponding to the “H₂O sticking probability”, issmall, but it can be predicted that the intensity of the adsorption willbe different.

Thus, according to research carried out by the inventors, the situationregarding the “H₂O sticking probability” is shown in the first place tobe fundamentally different from that regarding the “amount of H₂Oreleased”. There are present, separate from the adsorption sites whichcontribute toward the “amount of H₂O released” (referred to hereinafteras A sites), adsorption sites which have a lower density but a higheractivity (referred to hereinafter as B sites). It is clear that the Bsites contribute strongly to the “H₂O sticking probability”. Generally,the density of the B sites is of the order of 10¹² per cm², that is,about 0.1% of the number of atoms forming the surface, but it variesfrom one to two orders of magnitude, depending on the composition andstructure of the surface. Even though the B sites are at a lowerdensity, they have a higher activity so there is a high probability thatairborne H₂O will stick to these sites. Consequently, the contributionof the A sites which, even though they are present at a high density,have a lower activity, is small, and the magnitude of the “H₂O stickingprobability” is determined by the density of the B sites. However, thecontribution of the B sites to the “amount of H₂O released”,corresponding to a case where the amount adsorbed is high, is smallsince the density of the B sites is inevitably saturated.

The actual B sites are, for example, surface defects, and since thedefect density generally differs greatly according to the state of thesurface, there is also a corresponding marked difference in the “H₂Osticking probability”. Hence, a reduction of the defect density resultsin a reduction of the “H₂O sticking probability”. A reduction in the“H₂O sticking probability” is realized by removing the porous oxide filmwhich is present on the surface by heating under an ultra-high vacuum,as disclosed in Japanese Unexamined Patent Application (Kokai) H9-91606.The mechanism behind the “H₂O sticking probability” is thought by theinventors to be as described above.

Next, in order to confirm in practice the relationship between the“amount of H₂O released” and the “H₂O sticking probability”, the twovalues were measured for surfaces of stainless steels which had beensubjected to various types of surface treatment which are being usedindustrially at the present time. The measured results are shown in FIG.1. The “amount of H₂O released” is shown on the abscissa of the graphshown in FIG. 1 and the “H₂O sticking probability” is shown on theordinate. If there is a proportionality between the “amount of H₂Oreleased” and the “H₂O sticking probability”, then the measured points11 should be concentrated along the dotted line 12, but in practicethere is a very wide spread showing that there is no correlation betweenthe two values. This result supports the conclusions reached above.Furthermore, when seen from the viewpoint of surface treatment, the“amount of H₂O released” and the “H₂O sticking probability” are based ondifferent phenomena, and it is shown clearly that they each requiretheir individual countermeasure.

2. Reducing the “H₂O Sticking Probability” by the Deposition of SiliconOxide

In the course of carrying out the measurements described above it wasdiscovered that the “H₂O sticking probability” is reduced on surfaces towhich small amounts of C (carbon), S (sulphur) or Si (silicon, which isoxidized in practice and so it is really silicon oxide) and the likehave become attached by chance. However, in these cases again there isno marked change in the “amount of H₂O released”.

Thus, as an example, trace amounts of silicon oxide were deposited onthe surface of stainless steel, covering the surface, and the amountdeposited was controlled to vary the coverage. The relationship betweenthe silicon oxide coverage of the surface and the “H₂O stickingprobability” was investigated. Here, “the silicon oxide coverage of thesurface” signifies the percentage of the surface which is covered if thewhole area of the stainless steel is taken to be 1. A coverage of 100%is a state where the whole surface is finally covered after starting todeposit the silicon oxide film. The chemical vapor deposition method(CVD method) was used preferably for depositing the silicon oxide. Interms of the deposition conditions, tetra-ethoxysilane was used as thesource material and the stainless steel was heated to about 200 to 400°C., for example, in an atmosphere of tetra-ethoxysilane and oxygen. Theabovementioned silicon oxide coverage was measured using XPS(photoelectron spectroscopy) which is a method of surface analysis (thedetails are described in the illustrative examples). The resultsobtained are shown in FIG. 2.

Two graphs (A) and (B) are shown in FIG. 2, and graph (B) is anenlargement of the region 13 of graph (A). In graphs (A) and (B) in FIG.2, the silicon oxide coverage is shown on the abscissa and the “H₂Osticking probability” is shown on the ordinate. The characteristic 14shows the change in the “H₂O sticking probability” with respect to thesilicon oxide coverage. The probability in the “film formed” state 15(where the coverage is 100%), which is to say the “H₂O stickingprobability” of silicon oxide itself, is lower than the “H₂O stickingprobability” of the stainless steel itself in the “untreated” state 16(where the coverage is 0%). If the silicon oxide is deposited uniformly(selectively) on the surface and the “H₂O sticking probability” isreduced only in the covered regions, then the “H₂O sticking probability”of the whole surface should be an average value of the area ratio of thecovered part and the base stainless steel part. That is to say, the “H₂Osticking probability” between coverages of from 0 to 100% should lie onthe dotted line 17 which joins the point 15 which represents the “filmformed” state and the point 16 which represents the “untreated” state.However, the actual values are considerably below the dotted line 17.Moreover, it is also interesting that a value lower than the value forthe “film formed” state 15 is seen at coverages of from 40 to 80%.

The phenomenon described above can be interpreted in the following wayon the basis of the mechanism for the “H₂O sticking probability”conjectured above. At a coverage of less than 100%, the silicon oxide isnot deposited uniformly on the surface but selectively on theabovementioned B sites which contribute to the “H₂O stickingprobability”. Since the B sites are active sites it is natural that theairborne silicon source material (tetra-ethoxysilane) will be deposited,grow and degrade with the B sites as nuclei. As a result, the B sitesare inevitably embedded with inactive silicon oxide. Consequently, the“H₂O sticking probability” of the whole surface is greatly reduced witha coverage of less than 100% even though “film formation” has not beenachieved.

Moreover, when a silicon oxide film is actually formed over the whole ofthe surface, then new defects are formed in the surface of this film.These defects again provide active sites and so the “H₂O stickingprobability” inevitably rises again. Hence, B sites are deactivated bythe deposition of the silicon oxide film and the lowest “H₂O stickingprobability” is achieved at coverages of from 40 to 80% where no activesites are formed in the silicon oxide film.

A diagram of the abovementioned model is shown in FIG. 3. Here 20 is thestainless steel vacuum material. In FIG. 3, the “X” marks 21 shown onthe surface of the stainless steel 20 are the B sites which determinethe “H₂O sticking probability” and the small dots 22 are the A siteswhich determine the “amount of H₂O released”. The deposits 23 centeredaround the “X” marks are of silicon oxide (SiO_(x)). Most of the B sitesare embedded with the silicon oxide 23 and are deactivated because theyare covered with the silicon oxide 23. The A sites are not embedded butthey are of lower activity and they are not associated with the “H₂Osticking probability”. The B site density is about 0.1% of the A sitedensity. Accordingly, at a coverage of 50%, about 500 molecules ofsilicon oxide have been deposited on each B site. Silicon oxide islandscomprising such a number of molecules have grown from a single nucleusand so there are few surface defects. However, as the amount of siliconoxide deposited continues to rise, the islands grow and merge togetherto form a film over the whole surface and it is at this time that thenumber of defects increases with the merging surfaces as centers.

This can be illustrated in another way as follows. Cracks (correspondingto defects, B sites) are introduced into a concrete wall (correspondingto the surface). Dust (corresponding to H₂O) readily collects in thesecracks. If the cracks are then embedded with a caulking material(corresponding to the silicon oxide), then it becomes difficult for dustto collect. However, if the whole wall surface is covered with thecaulking material, then new cracks will form in the caulking materialsurface and dust will collect readily once again.

The lowering of the “H₂O sticking probability”, due to the deposition ofa trace amount of silicon oxide, can be understood in this way.

As indicated above, the method for the surface treatment of vacuummaterials of this invention is a method in which the stickingprobability of water on the surface of a vacuum material is reduced bydepositing a specified material (preferably a substance which containssilicon), such as silicon oxide, at least on the regions which determinethe “H₂O sticking probability” (the highly active B sites) on thesurface of the vacuum material, covering the regions, but with acoverage of less than 100%. In other words, the silicon oxide, or likematerial, is deposited on the surface in such a way that the coverage isless than 100%, and preferably with a coverage of from 30 to 90%, andmore preferably with a coverage of from 40 to 80%, as is clear fromgraph (A) in FIG. 2. It is possible with such a structure to reduce the“H₂O sticking probability” by some two orders of magnitude. Moreover,other merits (effects) are also realized on the basis of this generalprinciple.

First of all, the method of surface treatment of the invention has acoverage of less than 100% and so when compared with film depositionthere are advantages in terms of particles and gas release.

In other words, when depositing a film, and especially when it is beingdeposited from the outside, there is generally some concern about thestrength of attachment with the base. Peeling of the film occursnaturally as a result of the stresses within the film itself,differences in thermal expansion coefficients, and deformation of thebase, for example. Thus, the peeling of the film becomes a source ofparticles which are a serious problem when producing semiconductors andelectronic parts. Moreover, there is also some concern about thedenseness of the film. If the film is not dense enough, then not only isthere an increase in the number of defects which increases the “H₂Osticking probability” but there is also a risk that the amount of gasreleased, namely the gas which has been absorbed and diffused in thefilm itself, will also be increased. In practice, according to a studyof the reduction in the amount of gas released resulting from filmdeposition, it is reported that there is a marked difference in theamount of gas released depending on differences in the film depositionconditions even if the film composition is the same.

On the other hand, in the case of the method of surface treatment of thepresent invention, the amount of film deposited is only a trace amount,and the film is generally deposited only on the very active B sites.Accordingly, the problems with peeling and denseness are fundamentallyavoided.

The method of surface treatment of the present invention is not inprinciple based on the inherent properties of stainless steel andsilicon oxide but only in general on the nature of the “H₂O stickingprobability” on a solid surface and the nature of selective depositionof the source material. Hence, the method for the surface treatment ofvacuum materials of the invention is not limited to specific materialsbut can be used with many materials. In fact, its effect has also beenconfirmed with carbon and sulphur on a stainless steel surface and withsilicon oxide on an Al (aluminum) or Ti (titanium) surface.

EXAMPLES

A first embodiment of an apparatus for executing a method for thesurface treatment of vacuum materials according to the present inventionis shown in FIG. 4. A stainless steel vacuum material 32 is arranged ina generally tubular shaped reactor 31. A heater 33 is established on theoutside of the reactor 31 and the reactor 31 and the stainless steel 32are preferably heated to about 100 to 400° C. Gas delivery pipes 34 and35 are connected to the left end of the reactor 31, and a dew-pointmeter 36 is established on the right end. Oxygen (O₂) gas is supplied tothe gas delivery tube 34 via an O₂ mass flow controller 38 from an O₂gas cylinder 37, and the O₂ gas is delivered into the reactor 31. Theapparatus further includes a bubbling mechanism 39 andtetra-ethoxysilane 40 is housed in the container of the bubblingmechanism 39. Nitrogen (N₂) gas is supplied to the bubbling mechanism 39via a source gas mass flow controller 42 from an N₂ gas cylinder 41. Theleft end of the abovementioned gas delivery tube 35 is inserted into thebubbling mechanism 39. Moreover, 43 is a diluent gas mass flowcontroller, and 44 is the diluent gas pipe. By this means N₂ gas isintroduced directly into the reactor and so it is possible to controlthe concentration of source gas within the reactor. The structure whichintroduces N₂ gas directly into the reactor and controls the source gasconcentration is not an essential structure and it can be selected asrequired.

The stainless steel 32 which is to be surface treated is arranged in thereactor 31 and is heated with the heater 33. N₂ gas is discharged fromthe N₂ gas cylinder 41 under the control of the source gas flow ratecontroller 42. The N₂ gas passes through the liquid tetra-ethoxysilane40 in the bubbling mechanism 39 in the form of bubbles to form a gaswhich contains tetra-ethoxysilane vapor, and this is delivered via thegas delivery tube 35 into the reactor 31. Furthermore, 02 gas isdischarged from the O₂ gas cylinder 37 under the control of the O₂ massflow controller 38 and is delivered into the reactor 31 through the gasdelivery tube 34. The gaseous mixture of tetra-ethoxysilane, N₂ gas, andO₂ gas passes over the surface of the heated stainless steel 32 in thereactor 31. At this time, the tetra-ethoxysilane is decomposed, andsilicon oxide is deposited on the surface of the stainless steel 32. Thegas expelled from the reactor 31 is monitored in terms of its humidityby means of the dew-point meter 36.

The deposition method used above is generally known as the CVD method.Tetra-ethoxysilane is a type of organo-silicon compound and it is alsoknown as tetraethyl-ortho-silicate (TEOS). Its structure is shown inFIG. 5. The CVD method with tetra-ethoxysilane is used in semiconductorprocessing to deposit SiO₂ in the form of films from 100 to 1000molecules thick. The conditions for this processing withtetra-ethoxysilane alone involve a temperature of at least 700° C. WhenO₂ is supplied at the same time, a temperature of about 620 to 680° C.is used. When O₃ (ozone) is delivered at the same time, a temperature ofabout 400° C., and a deposition rate of some 1 to 10 molecular layersper second is obtained.

On the other hand, in the method for the surface treatment of vacuummaterials of this invention where the CVD method is used, selectivedeposition is required with deposition in amounts of less than amono-molecular layer. That is to say, it is necessary to deposit siliconoxide on all of the B sites while not forming a film over the otherparts so as to not form a complete film over the whole surface.Accordingly the processing conditions are set to a lower temperature fora longer period of time while supplying O₂ (oxygen) at the same time. Ina preferred embodiment, the temperature is set to about 100 to 400° C.,the O₂ mass flow rate is set to about 200 to 500 ml/minute, the massflow rate of N₂ gas which contains the tetra-ethoxysilane vapor is setto about 10 to 20 ml/minute, and the processing time is set to about 1to 10 minutes. Moreover, humidity is preferably maintained below a dewpoint of −50° C.

The conditions which should preferably be adhered to among theseconditions are the minimum temperature (100° C.) and the maximum dewpoint (−50° C.). The tolerance range for the other values is large, andin fact, it makes no great difference if separate N₂ gas is supplied atthe same time, or if the O₂ or tetra-ethoxysilane vapor concentrationsare reduced by an order of magnitude. Furthermore, the processing timeis shortened if the processing temperature is raised.

When carrying out an actual surface treatment, each flow rate and thetemperature are set. After ensuring that the conditions in the reactor31 are stable and the temperature is satisfactory, the stainless steel32 is introduced into the reactor 31. This state is maintained andprocessing is completed with the passage of the prescribed period oftime and then the stainless steel 32 is then taken out of the reactor31. The stainless steel is not subjected to any particular pre-treatmentor post-treatment, for example, other than the treatment indicatedabove. A sample of SUS304 of which the surface had been subjected toelectrolytic polishing (EP) and cleaning was used for the stainlesssteel 32 in the embodiment shown in FIG. 4, but these are not essentialconditions. In practice, experiments have been carried out with surfacesof SUS316L, and with surfaces which had been mechanically polished(buffed) and with surfaces on which an oxide film had been formed, andmore or less the same results were obtained.

The surface treated stainless steel 32 was subjected to measurement ofits “H₂O sticking probability” and its silicon oxide coverage using XPS(photoelectron spectroscopy). The “H₂O sticking probability” wasmeasured as the percentage of sticking when the surface which had beencleaned in an ultra-high vacuum was doped with 0.5 Langmuir (5×10¹⁴/cm²)of H₂O. In the XPS analysis the Kα line from an Al target was used asthe light source and, by setting the discharge angle of thephotoelectrons to 80° with respect to the normal, compositional analysisfor a layer of from 1 to 2 atoms from the surface was obtained. Theresults are shown by the solid black circles in FIG. 2.

Embodiments (experimental examples) of the method of surface treatmentof a vacuum material (stainless steel 32) in which the abovementionedtetra-ethoxysilane (TEOS) is used are indicated below in Table 1.

TABLE 1 B: Embodiment N₂ Carrier A: Treatment Conditions Gas Mass N₂Diluent TEOS Flow Gas Mass Treatment Temp. Exposure TEOS Conc. O₂ Conc.SCCM (= Flow O₂ Mass Flow Time ° C. torr · s torr torr cc/min) SCCM SCCMs (sec) 150 10³-10⁴ 10⁻²-10⁻¹ 10² Level 20 0 500   4 × 10⁴ Level Level200 10²-10³ 10⁻³-10⁻² 10² Level 20 2000 500 2.2 × 10⁴ Level Level 30010¹-10² 10⁻³-10⁻² 10² Level 20 1000 500 3.6 × 10³ Level Level 30010²-10³ 10⁻²-10⁻¹ 0 50 500 0 3.6 × 10³ level Level

Embodiments carried out with the common condition of dew point below−50° C. under the three temperature conditions of 150° C., 200° C. and300° C. within the aforementioned temperature range from 100 to 400° C.are shown in Table 1. The details of the embodiments at each temperatureare shown in column B on the right-hand side of Table 1. The embodimentsare described in terms of the N₂ carrier gas mass flow, the N₂ diluentgas mass flow, the O₂ mass flow and the treatment time. The N₂ carriergas passes through the bubbling mechanism 39 as described before and isdelivered into the reactor 31 carrying TEOS vapor. Moreover 2/760 of themass flow corresponds to the TEOS mass flow. Here in the proportion2/760, the 760 of the denominator corresponds to the set pressure of theabovementioned carrier gas, which is to say atmospheric pressure (760torr), and the 2 of the numerator corresponds to the saturated vaporpressure of the TEOS vapour (2 torr) resulting from the bubbling.Furthermore, in the embodiments N₂ diluent gas was delivered directlyinto the reactor by means of a diluent gas mass flow controller exceptwhen the treatment temperature was 150° C. The mass flow of gas isindicated in units of SCCM (ml(cc)/minute). In Table 1, the treatmentconditions are described generally in column A on the left-hand sidecorresponding to each embodiment at each temperature. The treatmentconditions are described in terms of the TEOS exposure (torr·s (sec)),the TEOS concentration (torr) and the O₂ concentration (torr). If themass flow of N₂ carrier gas is “a”, the mass flow of N₂ diluent gas is“b” and the mass flow of O₂ is “C”, then the TEOS concentration isobtained as 2a/(a+b+c) and the oxygen concentration is obtained as760c/(a+b+c). The formula 2a/(a+b+c) is derived by multiplying thesaturated vapor pressure 2 torr of the TEOS vapor by the dilutionproportions a/(a+b+c), and the formula 760c/(a+b+c) is derived bymultiplying the oxygen pressure, 760 torr, by the dilution proportionsc/(a+b+C), and the TEOS concentrations and O₂ concentrations wereobtained by means of these formulae. The TEOS exposure was obtained asthe product of the TEOS concentration and the treatment time. The TEOSexposure corresponds to the total number of TEOS particles reaching thesurface of the vacuum material per unit area in the treatment time whilethe TEOS concentration indicated in units of torr which indicatepressure corresponds to the number of TEOS particles per unit volume.

When the temperature was 300° C. in the above-mentioned embodiments,surface treatment in accordance with the invention could be carried outwithout oxygen, as indicated in the lower level in Table 1, since thetemperature was high.

A second embodiment of the construction of an apparatus for executingthe method of surface treatment of vacuum materials of the presentinvention is shown in FIG. 6. Parts which are essentially the same asparts described in FIG. 4 are indicated using the same reference numbersas in FIG. 4. The liquid 43 housed in the bubbling mechanism 39 ishexamethyldisiloxane. The construction apart from the change over fromthe tetra-ethoxysilane 40 described above to the hexamethyldisiloxane43, is the same as in the first embodiment described in FIG. 4. Thechemical formula for hexamethyldisiloxane 43 is shown in FIG. 7.

Hexamethyldisiloxane 43 is also a type of organo-silicon compound, andit is used in large quantities in silicone resins, silicone rubbers andsilicone oils which are all polymers which contain Si and O. Whencompared with tetra-ethoxysilane, hexamethyldisiloxane requires aslightly higher processing temperature of at least 200° C., and ahumidity of up to about −30° C. is permitted. It is thought that this isbecause tetra-ethoxysilane has a higher reactivity and inevitably reactswith H₂O in the space, and decomposition and deposition on the surfaceis inhibited. H₂O is generated from the stainless steel 32 and thereactor 31 during actual surface treatment and the temperature is liableto fall and so hexamethyldisiloxane is more useful from these points ofview.

The conditions other than the temperature and humidity are preferablythe same as in the first embodiment. In other words, the temperature isset to about 200 to 500° C., the O₂ mass flow rate is set to about 200to 500 ml/minute, the mass flow rate of N₂ gas which containshexamethyldisiloxane vapor is set to about 10 to 20 ml/minute, and thetreatment time is set to about 1 to 10 minutes. Furthermore the humidityis maintained at a dew point below −30° C.

As with the first embodiment, the results obtained are shown by the “X”marks in FIG. 2.

According to FIG. 2, there was no great difference between the resultswith the first embodiment and the results with the second embodiment. Inboth cases the “H₂O sticking probability” was greatly reduced when thesilicon oxide coverage was from 40 to 80%. The “H₂O stickingprobability” at this time had a small value at about 10⁻⁵.

Embodiments (experimental examples) of the method of surface treatmentof vacuum material (stainless steel 32) using the abovementionedhexamethyldisiloxane (referred to hereinafter as siloxane) are shownbelow in Table 2.

TABLE 2 B: Embodiments N₂ N₂ A: Treatment Conditions Carrier DiluentSiloxane Siloxane Treatment Gas Mass Gas Mass O₂ Mass Treatment Temp.Exposure Conc. O₂ Conc. Time After- Flow Flow Flow Time (° C.) torr · storr torr s oxidation SCCM SCCM SCCM s After-Oxidation 300 10²-10³10⁻¹-10⁰ 10² level 10²-10³ Yes 10 0 700 3.6 × 10³ Yes level level level300 10³-10⁴ 10⁰-10¹ 10² level 10³-10⁴ No 10 0 200 3.6 × 10³ No levellevel level

Embodiments carried out under conditions of dew point below −30° C. at atemperature of 300° C. within the aforementioned temperature range from200 to 500° C. are shown in Table 2. The details of the embodiments areshown in column B on the right-hand side of Table 2 in terms of the N₂carrier gas mass flow, the N₂ diluent gas mass flow, the O₂ mass flowand the treatment time. The N₂ carrier gas passes through the bubblingmechanism 39 as described before and is delivered into the reactor 31carrying siloxane vapor, and in this case the mass flow 55/760corresponds to the siloxane mass flow. Here in the proportion 55/760,the 760 of the denominator is as described before and the 55 of thenumerator corresponds to the saturated vapor pressure of the siloxanevapor (55 torr) resulting from the bubbling. Furthermore, in theembodiments the mass flow of N₂ diluent gas was set to 0, no diluent gasbeing used in this case. In Table 2 again the treatment conditions aredescribed generally in column A on the left-hand side corresponding toeach embodiment at each temperature. The treatment conditions aredescribed in terms of the siloxane exposure (torr·s (sec)), the siloxaneconcentration (torr), the O₂ concentration (torr) and the treatmenttime. The siloxane concentration and the O₂ concentration were obtainedin the ways described before, and the siloxane exposure was obtained asthe product of the siloxane concentration and the treatment time. Thesignificance of the exposure is the same as before.

Two cases, namely with after-oxidation (yes) and without after-oxidation(no), are described in the abovementioned embodiments. The conditions ofthe after-oxidation are, for example, O₂ concentration 760 torr,temperature conditions from 80 to 150° C. and treatment time from 0.5 to2 hours. The after-oxidation is an oxidation treatment carried out withthe vacuum material after subjecting said vacuum material to surfacetreatment. Oxidation is not carried out adequately when siloxane isused, and an after-oxidation is required.

The surface of the stainless steel 32 which had been subjected to themethod of surface treatment of the invention also had excellentstability after processing. Baking conditions which should be avoided soas not to allow the “H₂O sticking probability” to increase again havebeen indicated in Japanese Unexamined Patent Application (Kokai)H9-91606. In practice, baking is carried out for 50 hours under theseconditions, i.e., at an H₂O partial pressure of 5×10⁻⁵ torr (H₂ notadded) and a heating temperature of about 230° C. However, with asurface which has been surface-treated in accordance with the presentinvention there was virtually no change in the “H₂O stickingprobability”. These baking conditions are quite harsh conditions and sono problem at all is anticipated with the stability in use.

As indicated above, by means of the present invention it is possible toexecute a method for the surface treatment of vacuum materials which canin practice reduce the “H₂O sticking probability” satisfactorily.

In the above embodiments, a method in which the source gas and the O₂gas have been passed continuously at atmospheric pressure (normalpressure) has been used for bubbling, but other methods can be used.Thus, it is possible to make use of various types of liquid vaporizingapparatus, to use a reduced pressure or to carry out the treatment as abatch process. For example, when processing the inner surfaces of avacuum chamber which is of a large size or has a complicated shape, theinterior of the vacuum chamber can be temporarily set to a vacuum stateand then source material vapor and O₂ gas can be introducedsuccessively. When tetra-ethoxysilane in particular is being used, theprocessing temperature is low and so surface treatment in accordancewith the invention can be carried out satisfactorily after the vacuumapparatus has been completed.

In the embodiments described above, either tetra-ethoxysilane orhexamethyldisiloxane was used for the source material but otherorgano-silicon compounds and silicon-based gases such as SiH₄ (silane),for example, can also be used. Moreover, source materials other thansilicon, for example C (carbon) and S (sulphur) can also be used.Moreover, in cases where the presence of different elements is aproblem, the same element (substance) as the material surface can alsobe used. Not only stainless steel but a variety of other materials suchas Al (aluminum), Ti (titanium) and Cu (copper) can be used for thetreated vacuum material.

The method used to deposit the specified substance is not limited to theCVD method and physical vapor deposition methods (PVD methods) and otherliquid phase methods, for example, can also be used. Moreover, methodsin which elements which are included within the material areprecipitated out on the surface by heating can also be used.

Furthermore, in practice, the effect can be anticipated not only in avacuum apparatus which is used in a vacuum state in practice as a vacuumapparatus but also with materials where a similar reduction in the H₂Opartial pressure is required in the vacuum state, such as the materialsused in connection with highly pure gases for example.

Although only preferred embodiments are specifically illustrated anddescribed herein, it will be appreciated that many modifications andvariations of the present invention are possible in light of the aboveteachings and within the purview of the appended claims withoutdeparting from the spirit and intended scope of the invention.

What is claimed is:
 1. A surface treated vacuum material, comprising: asurface; and a deposited layer on the surface, the deposited layerincluding a substantially uniform distribution of molecules coveringless than 100% of the surface over which the molecules are substantiallyuniformly distributed.
 2. The material of claim 1, wherein the materialis stainless steel and the molecules are of an organo-silicon compound.3. A vacuum chamber comprising an interior surface made of the surfacetreated vacuum material of claim
 1. 4. The material of claim 1, whereinthe distribution of molecules covers only 40 to 80% of the surface. 5.The material of claim 1, wherein the deposited layer contains silicon.6. The material of claim 1, wherein the deposited layer is siliconoxide.
 7. The material of claim 1, wherein the vacuum material isstainless steel.
 8. The material of claim 1, wherein the deposited layeris formed using a CVD method.
 9. The material of claim 8, wherein theCVD method uses an organo-silicon compound.
 10. The material of claim 9,wherein the organo-silicon compound is tetra-ethoxysilane.
 11. Thematerial of claim 10, wherein the CVD method uses oxygen in theatmosphere and the CVD method is carried out in a temperature range of100 to 400° C., and the dew point is not more than −50° C.
 12. Thematerial of claim 9, wherein the organo-silicon compound ishexamethyldisiloxane.
 13. The material of claim 12, wherein the CVDmethod uses oxygen in the atmosphere and the CVD method is carried outin a temperature range of 200 to 500° C., and the dew point is not morethan −30° C.
 14. The material of claim 1, wherein the distribution isgenerally no greater than a single molecular layer.
 15. The material ofclam 1, wherein the vacuum material is part of a vacuum chamber.
 16. Thematerial of claim 1, wherein deposited layer reduces the H₂O stickingprobability of the vacuum material.